Which fish are highest in heavy metals?

November 14, 2025 •

4 min read

The US Food and Drug Administration (FDA) and Environmental Protection Agency (EPA) advise against consuming certain fish due to high mercury levels. Specifically, large, long-lived predatory species contain the highest amounts, which raises the question: which fish are highest in heavy metals?

Quick Summary

Larger predatory fish, such as shark, swordfish, and some tuna, bioaccumulate the most heavy metals, particularly mercury, due to their diet and longevity. Smaller fish typically contain lower concentrations.

Key Points

Apex Predators Accumulate the Most Metals: Large, long-lived predatory fish such as shark, swordfish, and king mackerel are highest in heavy metals, especially mercury, due to bioaccumulation.
Bioaccumulation is the Main Culprit: Mercury levels magnify up the food chain, meaning fish at the top of the food chain accumulate significantly more heavy metals than those at the bottom.
Smaller Fish are Safer Choices: Smaller, shorter-lived fish lower on the food chain, like sardines, salmon, and shrimp, contain much lower concentrations of heavy metals.
Vulnerable Populations Must Be Cautious: Pregnant women, breastfeeding mothers, and young children should avoid high-mercury fish entirely and limit moderate-mercury varieties.
Cooking Does Not Remove Heavy Metals: Cooking methods like boiling, frying, or grilling do not reduce the amount of mercury or other heavy metals bound to the fish's tissue.
Risk-Benefit Balance Favors Fish (with Care): The health benefits of eating fish, particularly the omega-3 fatty acids, outweigh the heavy metal risk for most people as long as consumption guidelines are followed.

Top Contenders: Fish Highest in Heavy Metals

Fish at the top of the marine food chain and with longer lifespans generally accumulate the highest concentrations of heavy metals, primarily mercury. To limit exposure, consider avoiding or reducing consumption of:

Shark: Consistently shows high mercury levels.
Swordfish: Often contains mercury near or above safety limits,.
King Mackerel: The larger variety has high mercury.
Tilefish (Gulf of Mexico): Noted for some of the highest recorded mercury levels.
Bigeye Tuna: Contains higher mercury than smaller tuna species.
Marlin: Similar to swordfish, it is high in mercury.

The Role of Biomagnification

Heavy metals like mercury enter waterways through natural and human sources. Bacteria convert inorganic mercury into toxic methylmercury, which enters the food chain. Biomagnification causes mercury concentration to increase at each level of the food chain, resulting in the highest levels in large, long-lived predators like sharks and swordfish that consume many smaller fish,. Cooking does not reduce mercury content.

Safer Alternatives: Fish with Low Heavy Metal Content

To enjoy seafood's benefits with less heavy metal risk, choose smaller, shorter-lived fish lower on the food chain. Good options include:

Wild Alaskan Salmon: High in omega-3s, low in mercury.
Sardines and Anchovies: Small, low-mercury fish.
Shellfish (Shrimp, Scallops, Oysters): Generally low in mercury.
Catfish (Farm-Raised): Often has very low mercury.
Canned Light Tuna: Made from smaller skipjack tuna with lower mercury than albacore,.
Atlantic Mackerel: The smaller variety is low in mercury.

Comparison: High- vs. Low-Mercury Fish

The table below compares typical mercury levels (in ppm) for various fish species:


Fish Species	Typical Mercury Level (ppm)	Why?
High-Mercury Options
Swordfish	~0.995	Large, long-lived predator.
Shark	~0.979	Apex predator.
King Mackerel	~0.730	Large, predatory fish.
Bigeye Tuna	~0.689	Large tuna species.
Low-Mercury Options
Canned Light Tuna	~0.128	Smaller skipjack tuna.
Cod	~0.111	Lower on the food chain.
Salmon (Wild Alaskan)	~0.022	Short lifespan, lower on food chain.
Sardines	~0.013	Very small, low-trophic-level fish.

Making Safe Consumption Choices

The nutritional benefits of fish, especially omega-3s, are important for most people when following consumption guidelines,.

General population guidelines:

Eat 2-3 servings (8-12 ounces) of diverse fish per week.
Focus on low-mercury "Best Choice" fish.
Limit moderate-mercury "Good Choice" fish (like halibut, snapper, albacore tuna) to one serving weekly.
Avoid "Choices to Avoid" (highest mercury) fish.

Special Considerations for Vulnerable Groups

Pregnant/breastfeeding women and young children are more sensitive to heavy metals, particularly mercury. Recommended actions include:

Avoiding shark, swordfish, king mackerel, and Gulf of Mexico tilefish.
Limiting canned albacore tuna to one 4-ounce serving weekly.
Eating 2-3 servings (8-12 ounces) total of lower-mercury fish weekly.

Conclusion: Informed Choices for a Healthy Diet

Understanding which fish are highest in heavy metals allows for informed dietary choices. By choosing smaller, lower-trophic-level species and following guidelines from health authorities like the FDA, you can enjoy the significant health benefits of seafood while minimizing heavy metal risk.

For more guidance, refer to the FDA and EPA's advice about eating fish.

What to Eat: A Quick Guide to Seafood Safety

Prioritize low-mercury fish like salmon, sardines, and shrimp. Varying your choices helps minimize exposure. Farmed options, like catfish, can also have lower heavy metal levels,,.

What to Avoid: The Riskiest Choices

The highest heavy metal levels are found in large, predatory, long-lived fish such as shark, swordfish, king mackerel, marlin, and bigeye tuna due to biomagnification,,.

Understanding Bioaccumulation

Heavy metals concentrate up the food chain. Organisms absorb them, and as larger predators consume these, the concentration increases, leading to high levels in species like shark and swordfish,.

Dietary Guidance for All

For a healthy diet, eat a variety of fish, focusing on low-mercury types. Moderation with higher-mercury species is important. The health benefits of omega-3s generally outweigh the risks when guidelines are followed,.

The Risks for Pregnant Women and Children

These groups are more susceptible to the effects of heavy metal exposure and should strictly follow guidelines to avoid high-mercury fish and limit moderate options to protect neurological development,,.

Why Canned Tuna Varies in Mercury

Canned tuna mercury levels depend on the tuna type. Canned 'light' tuna (skipjack) is lower in mercury than canned 'white' or albacore tuna (larger fish).

Farmed vs. Wild-Caught Heavy Metal Levels

Studies often show lower mercury in farm-raised fish due to controlled diets compared to wild-caught fish. Other contaminants and sustainability factors can vary.

The Takeaway: Eat Smart, Not Scared

Make informed choices by selecting a variety of smaller, lower-mercury fish and limiting high-mercury species. Following guidelines from sources like the FDA and EPA allows you to enjoy the health benefits of seafood safely.

Frequently Asked Questions

Large predatory fish contain more heavy metals, primarily mercury, due to a process called biomagnification. As these fish eat many smaller, mercury-containing fish throughout their long lives, the metal accumulates and becomes more concentrated at the top of the food chain,.

No, cooking fish does not remove heavy metals like mercury. This is because the metal is tightly bound to the fish's muscle tissue. Eating fish raw, cooked, or processed does not change its heavy metal content,.

Canned light tuna is typically made from smaller, younger skipjack tuna, which are lower in mercury. Albacore ('white') tuna comes from larger fish and therefore has a higher mercury content. Health authorities recommend limiting albacore consumption more strictly.

For low heavy metal content, recommended choices include small, low-trophic-level fish like salmon, sardines, anchovies, shrimp, catfish, and Atlantic mackerel. Eating a variety of these fish is recommended for health,.

Yes, but with caution. For pregnant women and children, health authorities recommend focusing on low-mercury fish while avoiding high-mercury species entirely. This allows them to receive crucial omega-3 fatty acids for development with minimal risk,.

Studies generally indicate that farm-raised fish, particularly those fed controlled diets, have lower mercury levels than their wild-caught counterparts. However, it's important to consider other factors like sustainability and other potential contaminants.

The FDA recommends that most people eat 8 to 12 ounces (two to three servings) of a variety of low-mercury fish per week. The specific amount of high-mercury fish should be limited to once a week or less.